The present invention relates to a laminate of an elastomeric substrate and a high density polyethylene (HDPE) having a melt index within a selected range. A preferred embodiment of the present invention relates to a seal having a low coefficient of friction and high abrasion resistance properties for an automotive vehicle.
The automotive industry uses elastomeric, thermoplastic and thermoplastic elastomeric materials, as well as combinations of such materials for many automotive applications. Each type of material has different physical properties and particular advantages for specific uses.
Elastomeric materials such as synthetic and natural rubbers as well as thermoplastic elastomeric materials are commonly used in the manufacture of automotive vehicles for seals, glass run channel, and other purposes. These materials have advantageous physical properties for sealing purposes. However, these materials have relatively high coefficients of friction and, in some cases, present a surface which has a relatively poor appearance and is difficult to color. For example, where these elastomeric materials are used in the manufacture of automotive glass run channel, provisions must be made to reduce the coefficient of friction to allow an associated glass panel to slide against the channel easily and without excessive wear on the elastomeric surface. One method of accomplishing this is to provide a coating on the elastomer or thermoplastic elastomer to provide a surface which has a low coefficient of friction and which is wear resistant. Traditionally, flocking was used to provide such a surface. In more recent years, various kinds of polymeric coatings such as polyethylene polymers have been used as coatings or layers.
Although efforts to coat or laminate a polyethylene material onto an elastomeric material have been carried out, the efforts have not been entirely satisfactory. For example, low and medium density polyethylene polymers are characterized by relatively low melting points. The low melting points allow the materials to be easily extruded but their uses are limited to applications where the polyethylene material will not encounter elevated temperatures. Thus, if such materials are applied to green rubber, the processing temperatures involved in later curing the rubber would cause such low melting point polyethylene polymers to become fluid and to flow out of the desired location of application. The class of polyethylene polymers known as ultra high molecular weight polyethylene polymers do not readily melt and are known and used in, for example, glass run channel. However, ultra high molecular weight polymers are expensive and difficult to process. For example, these polymers are preprocessed into the form of tapes because they cannot be extruded in a conventional extruder as they do not readily melt. They also are difficult to bond to rubber material.
As mentioned above, there have been efforts to utilize polyethylene materials to coat or layer onto elastomeric materials such as rubber. For example, U.S. Pat. No. 4,913,976 issued Apr. 3, 1990, to Brooks et al. describes a process for forming a laminate of a wear resistant thermoplastic and a weather resistant rubber. The thermoplastic layer, which can be polyethylene or polypropylene, is not melted but is processed at an ambient or a warm temperature by extruding through a crosshead die which places it into contact with the heated rubber. Mechanical bonding or fusion of the thermoplastic to the rubber is said to be achieved by melting the thermoplastic interface in contact with the rubber.
U.S. Pat. No. 5,007,202 issued Apr. 16, 1991, to Guillon discloses a guiding slideway for a motor vehicle window. The slideway is shaped to constitute a resiliently deformable toggle action linkage. The portions of the slideway which come into contact with the window are advantageously provided with a coating for facilitating sliding. The coating is preferably obtained by coextruding a polyolefin or a polytetrafluoroethylene together with the elastomer or plastomer of the slideway.
U.S. Pat. No. 5,014,464 issued May 14, 1991, to Dupuy et al. discloses a window pane sealing strip having a flexible reinforced glass-run channel. The strip includes a low friction finish which can be a coextruded low friction surface.
U.S. Pat. No. 5,183,613 issued Feb. 2, 1993, to Edwards discloses a process for the preparation of solventless, low friction, abrasion resistant coatings for elastomeric substrates.
While various processes for applying a low friction, wear resistant coating of polyethylene onto rubber are known, there remains a need for improvements in these processes. For example, the relatively high cost of ultra high molecular weight polyethylene and the difficulties encountered during processing of this type of polyethylene are disadvantageous. Other, lower molecular weight polyethylene materials can be easily processed but have high coefficients of friction and low abrasion resistance.
Therefore, and in accordance with the present invention, a polyethylene material is used which overcomes the aforementioned difficulties. Thus, a high density polyethylene with a load melt index within a particular specified range is extruded onto an elastomeric or thermoplastic elastomeric substrate to provide an improved laminate. The laminate of this invention can be made by a straightforward and economical process and the products thereof are particularly well suited for making automotive seals such as glass run channels, belt weather seals, colored rubber applications, and the like. The process uses economical materials, provides a good bond between the coating and the elastomer or thermoplastic elastomer, and provides a product having a coating or layer with a low coefficient of friction and excellent abrasion resistance and appearance as well as other desirable physical properties. Further understanding of the present invention will follow from the disclosure and claims taken in conjunction with the accompanying drawings.
The present invention provides, in a first aspect, a laminate assembly adapted for use as a weatherstrip seal. The laminate assembly includes an elastomeric substrate and a thin layer of a material that includes a particular type of polyethylene having certain physical characteristics. The thin layer has a thickness of less than 500 microns. The polyethylene exhibits a melt index of less than 10 grams per 10 minutes under conditions of 190 degrees centigrade, 2.160 kg total load and 298.2 kPa pressure. The polyethylene has a density of from about 0.940 to about 1.000 g/cm3.
In another aspect, the present invention provides a laminate assembly adapted for use as a weatherstrip seal in which the assembly comprises an elastomeric substrate and a thin layer of material disposed on and affixed to at least a portion of the substrate. The layer has a thickness of less than 500 microns and includes a certain polyethylene material. The polyethylene exhibits a melt index of greater than 5 grams per 10 minutes under conditions of 190 degrees centigrade, 21.6 kg total load, and 2982.2 kPa pressure. The polyethylene has a density of from about 0.940 to about 1.000 g/cm3.
In another aspect, the present invention provides a laminate product comprising (i) a substrate which is either natural rubber, synthetic rubber, a thermoplastic polyolefin, or a thermoplastic vulcanizate, and (ii) a high density polyethylene polymer layer disposed on the substrate. The polyethylene exhibits a melt index of less than 10 grams per 10 minutes under conditions of 190 degrees centigrade and 2.160 kg total load and 298.2 kPa pressure and a melt index of greater than 5 grams per 10 minutes under conditions of 190 degrees centigrade and 21.6 kg total load and 2982.2 kPa pressure.
In yet another aspect, the present invention provides a glass run channel that includes a substrate and a high density polyethylene layer disposed on the substrate. The substrate is selected from either natural rubber, synthetic rubber, a thermoplastic polyolefin, or a thermoplastic vulcanizate. The polyethylene exhibits a melt index of less than 10 grams per 10 minutes under conditions of 190 degrees centigrade, 2.160 kg total load, and 298.2 kPa pressure. The polyethylene also exhibits a melt index of greater than 5 grams per 10 minutes under conditions of 190 degrees centigrade, 21.6 kg total load, and 2982.2 kPa pressure.
In yet another aspect, the present invention provides a belt weatherstrip comprising a substrate, which may be one or more of a natural rubber, synthetic rubber, thermoplastic polyolefin, and thermoplastic vulcanizate, and a high density polyethylene layer. The polyethylene has a melt index of less than 10 grams per 10 minutes under conditions of 190 degrees centigrade, 2.160 kg total load, and 298.2 kPa pressure. The polyethylene also exhibits a melt index of greater than 5 grams per 10 minutes under conditions of 190 degrees centigrade, 21.6 kg total load, and 2982.2 kPa pressure.
Furthermore, the present invention also provides a method of making an extruded laminate comprising co-extruding a substrate and a certain high density polyethylene. The substrate may be synthetic rubber, natural rubber, thermoplastic polyolefin, or a thermoplastic vulcanizate. The polyethylene has a particular melt index as previously described.